The present invention generally relates to a sputtering apparatus and a film forming method using the sputtering apparatus.
As a method for producing a dielectric film (such as oxide film), a production method by means of reactive sputtering, in which active gas is introduced to a sputtering space and sputtering materials obtained from a target react to the active gas and a compound film is deposited, has been known.
In this reactive sputtering, a cathode is usually disposed in parallel with a substrate. Thus, sputtering particles that are discharged perpendicularly from a target on the cathode are incident on the substrate. Since such sputtering particles have high energy, there has been a problem in that, when a dielectric film is formed on the substrate, the dielectric film becomes damaged.
Conventionally, in order to solve this problem, a producing method by means of facing target sputtering has been proposed. In this producing method, a pair of targets are disposed so as to face each other with a space between them, and Penning discharge is applied by generating a magnetic field in a direction perpendicular to the targets (Patent: JP S62-56575B).
Reference numeral 110 in FIG. 7 indicates a conventional facing target sputtering apparatus. The sputtering apparatus 110 is provided with a vacuum chamber 111, and in the vacuum chamber 111, two targets 121a and 121b are disposed such that their surfaces are in parallel and face each other with a certain space between them. The back faces of the targets 121a and 121b are mounted to cathode electrodes 122a and 122b, respectively. Magnetic members 115a and 115b are disposed on the back face of the cathode electrodes 122a and 122b. The magnetic members 115a and 115b are configured by installing ring-shaped magnets 123a and 123b to yokes 129a and 129b. 
The magnets 123a and 123b are respectively disposed that one of the magnetic poles thereof is directed toward the targets 121a and 121b and the other magnetic pole thereof is directed in the opposite direction, to the targets. Furthermore, the magnets 123a and 123b are disposed in such a manner that different polarity of magnetic poles of the magnets 123a and 123b are directed to the targets 121a and 121b. 
In other words, if the north pole of the magnet 123a is directed toward the target 121a, the south pole of the other magnet 123b is directed toward the target 121b. Since the magnets 123a and 123b are in a ring shape, magnetic lines of force are formed in a cylindrical shape between the magnets 123a and 123b. 
The inside of the vacuum chamber 111 is evacuated by vacuum evacuation system 116; sputtering gas is introduced from gas feeding system; and voltage is applied to the target 121a and 121b. Consequently, plasma of sputtering gas is generated in the space interposed between the targets 121a and 121b so that the surface of the targets 121a, 121b are sputtered.
An object to be film formed 113 is disposed lateral to the space sandwiched between the targets 121a and 121b. A film is formed on the surface of the object to be film formed 113 by the sputtering particles that are obliquely sputtered from the targets 121a and 121b in order to discharge to the inside of the vacuum chamber 111.
With the sputtering apparatus 110, particles having high-speed energy can be confined between a pair of the targets using the magnetic lines of force in a cylindrical shape. Thus, it is possible to prevent incidence of high-speed energy particles on a substrate, and thereby a film with less damage can be produced.
Although only inert gas is used as sputtering gas in conventional sputtering, in the above-mentioned reactive sputtering, active gas is used in addition to inert gas as sputtering gas, and a film is formed with a reacted product of the solid particles that are sputtered from the targets and the active gas.
When a thin oxide film is to be formed, oxygen gas as active gas is simultaneously introduced to sputtering gas. For this reason, the surfaces of the targets become oxidized; and, furthermore, a dielectric film is deposited on a protective plate, a ground shield, and others so that abnormal arc discharge may occur frequently.
In order to eliminate abnormal arc discharges, it has been conventionally proposed that an alternating current electric field of which phase are shifted by 180 degrees be applied to the two targets facing each other with a (JP H11-29862A).
However, even if the alternating current electric field is applied, when a dielectric film is continued to be formed, a dielectric film is deposited on the target surface, the protective plate, the inner walls of a cathode box (sputtering chamber), and others; and abnormal arc discharges occurred.
Furthermore, there has been a problem in that when the dielectric film is continued to be formed and the dielectric film is deposited on the entire inner walls of the cathode box, plasma which search a ground potential spouts from inside of the cylindrical magnetic lines of force into the space that is on the side where the substrate is disposed, and thus the substrate is damaged by plasma. These problems are disclosed in JPB S62-56575 and JPA H11-29862, for example.